The present invention relates to a timer arrangement and, more particularly, to a fuel injection timer for internal combustion engines, wherein a shaft of a fuel injection pump is rotated relative to a drive shaft connected to the internal combustion engine as a function of a rotational speed of the internal combustion engine.
A fuel injection timer of the aforementioned type may be provided with a plurality of oscillating bodies disposed between first tracks connected to a drive shaft of an internal combustion engine and a second track connected to a fuel injection pump shaft, with the tracks geing disposed in opposed pairs, and with the oscillating bodies each transmitting a portion of a drive torque of the fuel pump and moving from an inner end position at a low engine rotational speed to an outer end position at a maximum rotational speed under an influence of centrifugal forces and counteracting spring forces resulting in the oscillating bodies being displaced over a distance and, thereby, by virtue of a slope created by the tracks, effecting a relative rotation between the two shafts with a timing curve for a fuel injection which corresponds to a favorable combustion cycle for the internal combustion engine.
In injection timers wherein the oscillating bodies, functioning as flyweights, are connected, to reduce the load, in parallel, the oscillating bodies transmit only a portion of the torque. A disadvantage of this type of injection timer resides in the fact that, if the tracks of the injection timer are only provided with a relatively gentle or small slope, only a relatively small rotational angle may be produced. If the slope of the tracks is increased, the rotational angle can be increased; however, at the same time, no automatic locking between the tracks and the oscillating bodies or flyweights exists so that a displacement of the flyweights or oscillating bodies inwardly is caused by the high torque peaks of the fuel injection pump, especially at high rotational speeds and loads on the internal combustion engine thereby resulting in large quantities of fuel being injected. A disadvantage of the displacement of the flyweights resides in the fact that an unfavorable change in the timing curve for the fuel injection results, which timing curve is required to achieve favorable combustion in the respective cylinders of the internal combustion engine.
If the tracks and associated oscillating bodies or flyweights are not constructed so as to be automatically self-locking or self-suppressing, when the natural frequencies of the injection timer correspond to excitation frequencies, oscillation state may occur in the injection timer which cause premature destruction of the tracks and the oscillating bodies or flyweights and also cause undesirable displacement of the oscillating bodies or flyweights inwardly and outwardly whereby a change in the timing curve is likewise produced.